Strasbourg

On August 3rd 1947, a major race was held in Strasbourg. It was called the Grand Prix d'Alsace.

Two decades and more earlier, races had been run on an 8 mile circuit to the south-west of the town but I have just realised that this was not where the 1947 race was run. The circuit used for that event was 2.25 miles in length.

I have searched the internet, including French language sites, but have so far failed to learn anything about this track.

The race was in a part of Strasbourg called Neudorf.
Departure Route du Rhin than turn to Avenue Aristide Briand, Rue Jean Jaures,
Route du Polygone and back to Route du Rhin.
Only Route du Rhin has changed since and not much...

The Route du Polygone actually does not exist between the Rue Jean Jaures and the Route du Rhin. In fact, if you check the historical imagery on Google Earth, in 2007 the area appears to be a lorry park or something similar, whereas now it is just an open area with grass and trees.

However, Google offers an aerial view from 1943! In that one, there does appear to be a road that is an extension of the Route du Polygone, running right across the space where there is no road now.

Using that road (only 4 years before the race in question) my circuit line turns out to be 3,811 meters - the distance shown on the race result is 3,626, so we are out by 185 meters. A sizeable amount but then again, there is little doubt that we ARE in the right place.

Yes, uechtel, that's where I started. The interesting thing is that the map you linked to shows the Route du Polygone running straight across that area I mentioned. But when you switch to the satellite view, there is no road.

If I modify my line to follow the imaginary road across that area, my circuit length comes down to 3,701, which is only 75 meters out, so as Rudi says, I reckon we are about there.

This is great news - it means I will be able to go ahead with my Grand Prix d'Alsace next year, confident that I have the circuit plan just about right.

Don't forget that circuits are traditionally measured on the 'racing line,' roughly 1m from the inside edge on bends and on the common tangent joining these arcs, while mapping sites measure on the centreline of the road and may even measure between intersection pionts of the straights rather than following the kerb. So the [map] measured length will always be less than the [racing line] measured length. Can't say by how much it will vary depending on how wiggly a track is.

Then again, Duncan, back in 1947, the circuit may well have been measured by someone walking around, counting his steps then 'doing the math'.

Maybe all the rulers were destroyed during the war.

In all seriousness they may well have used a surveyor's wheel a calibrated wheel on a stick with a rotation counter, a precision version of the cyclometer which you coukld fix to the front fork and wheel of your bicycle to measure how far you'd gone (at least until you forgot it was there and broke it when you laid your bike down).

The satellite picture and the labels clearly don't match. You can see that the Route du Rhin leads into a tunnel. My guess would be that this is a relatively new construction and the Google map labels still show the old arrangement of the streets. The heavy construction work north of the Route de Rhine indicates that the whole area was remodeled. Perhaps, and that's another guess, to transform a former harbour into a new town quarter.

The satellite picture and the labels clearly don't match. You can see that the Route du Rhin leads into a tunnel. My guess would be that this is a relatively new construction and the Google map labels still show the old arrangement of the streets. The heavy construction work north of the Route de Rhine indicates that the whole area was remodeled. Perhaps, and that's another guess, to transform a former harbour into a new town quarter.

Google Earth has a 1943 aerial photo. There is a slight difference to the layout at the western end, but otherwise the roads seem identical.

Google Earth has a 1943 aerial photo. There is a slight difference to the layout at the western end, but otherwise the roads seem identical.

Of course I was only talking about the western end, the "missing" part of Rue du Polygone. I cannot access that 1943 aerial picture, so I wonder what you mean by "slight difference". Hard to believe that the Route du Rhin tunnel would have existed in 1943.

Just to make my point clear: I do not doubt that this "missing part" of Rue du Polygone once was there and was used as part of the racetrack. I just think the area has been remodeled when the tunnel has been build. That could explain why the "missing part" has vanished in the current satellite foto but is still included in the Google maps labels.

In all seriousness they may well have used a surveyor's wheel a calibrated wheel on a stick with a rotation counter, a precision version of the cyclometer which you coukld fix to the front fork and wheel of your bicycle to measure how far you'd gone (at least until you forgot it was there and broke it when you laid your bike down).